1. Field of the Invention
A fastening for a round shank chisel on a road scraper or the like, wherein the round shank chisel has a chisel head and a chisel shank, the chisel head rests with a contact surface on a wear-protection disk, which is supported on a chisel holder, and the chisel shank is inserted into a receiver bore of the chisel holder.
2. Description of Related Art
Such a fastening is known from German Patent Reference DE 34 08 209 A1. With this fastening, the chisel shank of the round shank chisel is clampingly maintained in the receiver bore of the chisel holder with a clamping sleeve. The receiver bore is widened in the direction toward the chisel head. A ring element is positioned into this widening. The ring element has a circumferential collar, which projects past the top of the chisel holder. The collar is triangular in cross section. The collar engages a receiver groove, also triangular, of the chisel head. The chisel head is supported on the collar. With this arrangement dirt can be prevented from penetrating the area formed between the chisel head and the chisel holder and from subsequently entering the receiver bore. The ring element is made of a hard alloy. The round shank chisel rotates in the receiver bore when the tool is used. This causes considerable abrasion in the receiver groove of the chisel head. Because the ring element is made of a hard alloy, very strong abrasion results. The receiver groove is ground smooth after a short time of use, and the chisel head then is seated on the chisel holder which negatively affects the rotating ability of the round shank chisel that can cause the round shank chisel to seize.
It is one object of this invention to provide a fastening for a round shank chisel of the type described above but wherein the penetration of dirt into the receiver bore is dependably prevented, and wherein a rotating ability of the round shank chisel is not negatively affected during the entire service life of the round shank chisel.
This object is attained with a chisel holder that has a protrusion or a circumferential molding extending around the receiver bore. A wear-protection disk has a circumferential groove or a circumferential shoulder. In the assembled state of the round shank chisel, the protrusion or the molding of the chisel holder engages the receiver groove or the shoulder of the wear-protection disk.
A sort of a labyrinth is created between the contact surface of the chisel holder and the wear-protection disk by the receiver groove and the shoulder, which prevents the penetration of scraped-off material into the receiver bore. At the same time the rotating ability of the round shank chisel is not negatively affected, because the round shank chisel can be supported by its chisel head flat on the level wear-protection disk.
In a preferred embodiment of this invention, a protrusion is designed trapezoidal in cross section and has two lateral flanks, which extend at an angle with respect to a center longitudinal axis of the round shank chisel which, facing the wear-protection disk, are connected by a flat support section. The receiver groove of the wear-protection disk is also designed trapezoidal in cross section and rests with a contact surface on the support section. The support of the wear-protection disk over a large surface permits the transmission of high stresses occurring during work.
To align the wear-protection disk with the receiver bore, on its end area facing the chisel head, the receiver bore has a widening, against whose boundary face the wear-protection disk rests with a centering section.
In this case the centering section can be a part of the receiver groove, so that the effective contact surface is further enlarged for support and dissipation of introduced forces.
To simplify the mounting of the wear-protection disk on the round shank chisel, the chisel shank is inserted into a passage in the wear-protection disk, and on its area facing the chisel head, the passage has a widening. Alternatively or additionally, the free end of the chisel shank can also have a bevel, possibly with a phase.
A simple manufacture of the wear-protection disk can be achieved, for example, if it is produced as a punched and bent element from a disk-shaped blank, with an outer edge having a circumferential bent portion in the manner of a dish. The bent portion in a radially outwardly direction borders the receiving groove.